Preparation of unsaturated hydrocarbons from oxygen-containing organic materials



United States Patent PREPARATEQN 0F UNSATURATED HYDRQAR- EQNS FRGMOXYGEN-CQNTAENENG URGANEC MATERIALS Wiiiiam M. Hearon, San Rafael,Calif., and David W.

Goheen and John T. Henderson, Camas, Wash, assignors to Crown ZelierbachQorporation, San Francisco, Caiifi, a corporation of l evatia NoDrawing. Filed May 4, 1961, Ser. No. 107,658

20 Claims. (Ci. 260-679) This invention relates to the preparation ofunsaturated hydrocarbons from oxygen-containing organic materials. Itpertains particularly to the preparation of low molecular weight,unsaturated hydrocarbons such as acetylene and ethylene.

While it is well known to prepare acetylene, ethylene and other lowmolecular weight, unsaturated hydrocarbons by various thermal processesfrom carbonaceous and hydrocarbonaceous raw materials such as coal andpetroleum, it heretofore has not been known to prepare such products ona commercial scale from oxygen-containing starting materials such aslignin, lignocellulose and the carbohydrates. Indeed, in view of thehigh degree of reactivity of elemental oxygen at elevated temperatures,it has been considered impossible to use such starting materials for theindicated purpose in view of the likelihood of forming oxygen-containingend products.

The desirability is readily apparent of providing a commercial processfor the large scale production of highly useful industrial chemicalssuch as acetylene and ethylene from a replenishable source such as woodand from waste products such as bark and pulp mill spent liquors.

Accordingly, it is the general object of the present invention toprovide a commercial process for the production of unsaturatedhydrocarbons such as acetylene and ethylene from raw materialscontaining a high percentage of oxygen, such as lignin, lignocellulose,and the carbohydrates.

Afurther important object of the invention is the provision of a processfor making unsaturated hydrocarbons from pulp mill spent liquors, whichprocess may be operated as an adjunct of paper mill pulping procedures,without abnormal loss of pulping chemicals, and without destroying thedelicate chemical balance which must be preserved during the pulpingprocess.

We now have discovered that, unexpectedly and con trary to the teachingsof the prior art, unsaturated hydrocarbons such as acetylene andethylene may be obtained in yields of up to 50% of the theoretical by aprocess which, broadly considered, comprises reducing the material tofinely divided form, heating it rapidly in a substantially inert gaseousenvironment to a selected temperature of at least 1000 F., maintainingit at the selected temperature until a substantial proportion of it hasbeen converted to a reaction product including the desired unsaturatedhydrocarbons, rapidly cooling the reaction product, and separating theunsaturated hydrocarbon components from it.

As an important modification of the foregoing procedure, it may becarried out as an adjunct of paper mill pulping procedures. In this casethe process comprises cooking lignocellulose in an aqueous medium with apredetermined proportion of an inorganic lignocellulose pulping agentfor substantial separation of the lignin from the cellulose, separatingthe resulting cellulosic pulp from the residual spent liquor, separatingthe inorganic salt content of the liquor and returning it to the pulpingof a further quantity of the lignocellulose, separating the lignincontent of the liquor as a finely divided solid, and then pyrolyzing thesolid in a substantially inert gaseous en- 3,148,227 Patented Sept. 8,1964 vironment as set forth above. In this way the unsaturatedhydrocarbon products may be manufactured Without abnormal loss ofpulping chemicals and without destroying the material balance in thedigesters.

As raw materials for the process of our invention, there may be employeda diversity of oxygen-containing substances. Thus the alkali lignins,including soda lignin and kraft lignin, are eminently suitable for thepresent purpose. These preferably are treated first for removal of theirinorganic salt content, which then may be cycled to the chemicalrecovery system of the pulp mill.

In addition, the sulfonated lignins contained in sulfite spent liquormay be employed, keeping in mind that the sulfur contained in suchliquor may serve as a hydrogen scavenger during the pyrolysis reaction,thus reducing correspondingly the yield of unsaturated hydrocarbonproducts. Hence if use of lignins of this class is contemplated,

their desulfonation by reaction with lime, or otherwise, is recommendedas a preliminary treatment.

Whatever their source, the pulping spent liquors are evaporated orchemically treated for separation of the solid lignins. These then aredried sufficiently to convert them to a finely divided powder which maybe handled easily.

The lignocellulose materials such as the woods and barks of various treespecies, and various non-woody plant materials such as bagasse, strawand cornstalks, are also applicable broadly to the purposes of thepresent invention. When using these materials they first are dried, ifdesired, and reduced to finely divided form in any suitable grinding orcomminuting apparatus. Although the degree of subdivision is variable,depending upon the nature of the materials and the reaction conditions,in general it is preferred to reduce them to a particle size of not over20 mesh, U.S. Sieve Series.

The various carbohydrates, such as sugars, starch and, particularly,cellulose, also are applicable as starting materials for the presentlydescribed process. In this case also the materials first are reduced toa dry powder, preferably one having a particle size of not over 20 mesh,U.S. Sieve Series.

The selected starting material is introduced into a reaction zonecontaining a substantially inert, or at least nondetrimental, gas suchas helium, carbon monoxide, argon, or neon. Nitrogen also may beemployed, although in this case hydrogen cyanide may be formed as aby-product. Preferably the solid material is introduced into thereaction zone by entraining it in a stream of the selected gaseouscarrier.

The reaction zone may be heated to the desired level and in any suitablemanner, as by partial combustion of the reacting material, indirectcombustion, electrical resistance heating, electric arc heating, etc.

It is critical to the success of the presently described process thatthe temperature of the material be elevated rapidly in the reaction zoneto a level of at least 1000*" F. If this is not done, the usualoxygen-containing pyrolysis products of lignin and woody materials areobtained. These include tars, resins, pyroligneous acids and the like.

However, when the temperature is elevated rapidly to the indicatedlevel, there is produced a reactive mixture of carbon and hydrogenatoms, radicals and ions which will interact with each other to produceethylene or acetylene as principal products depending primarily upon thereaction temperature. Thus temperatures of between l000 F. and about2200 F. favor the production of ethylene. At temperatures of from about2200 F. to 3500 F. substantial amounts of acetylene are formed.

These two desired end products, however, have a marked tendency todecompose at the reaction temperature into carbon and hydrogen. Thus itbecomes critically essential to carry out the reaction as a flashreaction, or at least to restrict severely the dwell time of the reactants in the reaction zone to a period of from seconds to one of nomore than 10 seconds. When producing acetylene, the preferred dwell timeis from 10- second to 0.5 second. When producing ethylene it is from 10second to 2 seconds. In both cases the reaction period will varyinversely with the reaction temperature.

At the conclusion of the reaction period the reaction mixture is cooledrapidly, preferably by quenching it in a spray of Water or other liquid,or by passing it through a heat exchanger cooled eflioiently by water orother cooling medium.

After cooling, the gaseous components of the reaction mixture areseparated from any suspended carbon which may have been formed. Theacetylene and ethylene products are recovered and separated from eachother by any of the methods conventionaly employed for this purpose.

The process of the invention is illustrated by the following examples,wherein the yields are expressed as ields by weight, based on the weightof the oxygen-containing starting material.

Example 1 A 4-way T reactor was fitted with two tungsten wires connectedto a high voltage source. An arc was struck between the wires. Drypowdered kraft lignin obtained by the acidification of kraft blackliquor was blown through the are using helium as a carrier gas. Themaximum temperature of the arc was about 3600 F. An analysis of thegaseous product indicated an acetylene yield of 14%.

The foregoing procedure was repeated, using the following as startingmaterials, and with the indicated yields of acetylene: (a)lime-desulfonated calcium-base sulfite spent liquor, 12.5%; (b) finelypowdered Douglas fir wood, 13%; and (c) powdered alpha-cellulose, 14.5%.

Example 2 This example illustrates the application of resistance heatingto the presently described process.

In a 4-way T tube reactor was placed a coil wound with A diameter No. 28tungsten wire. The coil was connected to copper wire sealed into thesystem and a current of 500 watts passed through the coil, thetemperature of which reached a level of from 35004500 F.

Precipitated kraft lignin was blown onto the coil using helium as agaseous carrier. The gases were removed from the reaction zoneimmediately and collected over saturated brine. An acetylene yield of23% was obtained.

Example 3 A furnace consisting of a 1" ceramic tube surrounded by a A"layer of flake graphite held in place by an alumina cylinder was heatedwith Rf current. The heating zone was 5" long and was packed loosely forabout one-half its distance with broken ceramic. Water cooled coppertubes communicated with the ceramic tube at its upstream and downstreamends. Means were provided for admitting the powdered feed in an inertcarrier gas at a controlled flow rate, thereby enabling variousresidence times in the furnace.

With the temperature at 2900 F. and a helium flow rate of 2700 ml./min.,2.6 grams of dry precipitated kraft lignin were added to the furnace in30 seconds. The gaseous product was collected over water. Analysisindicated an acetylene yield of 8.6% and an ethylene yield of 2.5%.

Example 4 The procedure of Example 3 was repeated, heating the furnaceto 2100 F. 2.6 grams of dry, precipitated kraft lignin were added in 30seconds with a helium flow rate l of 2700 nil/min. In this case a 3.5%yield of acetylene and a 7.2% yield of ethylene were obtained.

Example 5 The procedure of Example 3 again was repeated, with thefurnace heated to 2600" F. and the helium flow rate adjusted to 2700mL/min. Under these conditions, 1.8 grams of powdered Douglas fir woodwere passed through the system in about 2 minutes. An acetylene yield of13% and an ethylene yield of 4.6% were obtained. Bubbling the gaseousproduct through silver nitrate test solution resulted in the formationof a characteristic precipitate of solid silver carbide-silver nitrate.

Example 6 Into the furnace of Example 3 heated to 2700 F. using a heliumflow of 4000 ml./min. were passed 2 grams of -mesh whole bagasse inabout 3 minutes. An acetylene yield of 15% was obtained.

Example 7 Using the furnace and conditions of Example 3, 2 grams of60-mesh Douglas fir bark was passed through the furnace. A yield of12.5% acetylene was obtained.

Example 8 A plasma was made by passing argon through a 1 quartz tubesurrounded by a 17-turn water-cooled copper tubing coil connected to aradio frequency generator. The temperature of the plasma was from 4000F. to 5000 F. Careful addition of 0.3 gram powdered bagasse into theplasma in about 3 minutes resulted in collection of a 17% yield ofacetylene. There was no evidence of the formation of any ethylene ormethane.

Thus it is apparent that by the present invention we have provided aprocess for making unsaturated hydrocarbons such as ethylene andacetylene from oxygen-com taining raw materials such as lignin,l-ignocellulose and the carbohydrates. The process is applicable on alarge commercial scale and makes useful various categories of materials,notably pulping spent liquors, sawdust and bark, which are available invery large quantities and normal-1y present a disposal problem. Inaddition, the process may be included in normal pulp mill recoveryprocedures without disturbing material balances or causing abnormal lossof pulping chemicals.

Having thus described our invention in preferred embodiments, we claimas new and desire to protect by Letters Patent:

1. The process of preparing unsaturated hydrocarbons of the groupconsisting of acetylene and ethylene from oxygen-containing organicmaterials comprising at least one member of the class consisting of thelignins, the lignocelluloses, and the carbohydrates, said processcomprising: reducing the material to a finely divided form, rapidlyheating the material in a substantially inert gaseous environment to aselected temperature of at least 1000 F, maintaining the material at theselected temperature for a time of from 10' seconds to about 10 seconds,thereby converting a substantial proportion of it to a reaction productincluding a substantial proportion of unsaturated hydrocarbon, rapidlycooling the reaction product, and separating the unsaturated hydrocarboncomponent therefrom.

2. The process of claim 1 wherein the oxygen-containing organic materialcomprises a lignin.

3. The process of claim 1 wherein the oxygen-containing organic materialcomprises a lignin-containing pulping spent liquor.

4. The process of claim 1 wherein the oxygen-containing organic materialcomprises soda lignin.

5. The process of claim 1 wherein the oXygen-contain ing organicmaterial comprises kraft lignin.

6. The process of claim 1 wherein the oxygen-containing organic materialcomprises lignocellulose.

7. The process of claim 1 wherein the oxygen-containing organic materialcomprises the wood of trees.

8. The process of claim 1 wherein the oxygen-containing organic materialcomprises the barkof trees.

9. The process of claim 1 wherein the oxygen-containing organic materialcomprises non-woody plants.

10. The process of claim 1 wherein the oxygen-containing organicmaterial comprises bagasse.

11. The process of claim 1 wherein the oxygen-containing organicmaterial comprises a carbohydrate.

12. The process of claim 1 wherein the oxygen-containing organicmaterial comprises cellulose.

13. The process of claim 1 wherein the material is heated to atemperature of from 10002200 F. and wherein the principal unsaturatedhydrocarbon product comprises ethylene.

14. The process of claim 1 wherein the material is heated to atemperature of from 2200-3500 F. and wherein the principal unsaturatedhydrocarbon product comprises acetylene.

15. The process of claim 1 wherein the reaction product is cooledrapidly by quenching it in water.

16. The process of making unsaturated hydrocarbons of the groupsconsisting of acetylene and ethylene which comprises cookinglignocellulose in an aqueous medium with a predetermined proportion ofan inorganic lignocellulose pulping agent for substantial separation ofthe lignin from the cellulose, separating the resulting cellulosic pulpfrom the residual spent liquor, separting the inorganic compound contentof the liquor and returning it to the pulping of a further quantity oflignocellulose, separating the lignin content of the liquor as a finelydivided solid, rapidly heating the solid lignin in a substantially inertgaseous environment to a selected temperature of at least 1000 F.,maintaining the lignin solids at the selected temperature for a time offrom 10- seconds to about 10 seconds, thereby converting a substantialproportion thereof to a reaction product including the unsaturatedhydrocarbon, rapidly cooling the reaction product, and separating theunsaturated hydrocarbon therefrom.

17. The process of claim 16 wherein the inorganic lignocellulose pulpingagent comprises a kraft pulping agent.

18. The process of claim 16 wherein the inorganic lignocellulose pulpingagent comprises a soda pulping agent.

19. The process of claim 16 wherein the inorganic lignocellulose pulpingagent comprises a sulfite pulping agent.

20. The process of claim 16 wherein the inorganic lignocellulose pulpingagent comprises a sulfite pulping agent and including the step ofdesulfonating the spent liquor preliminary to separating the ligninsolids.

References Cited in the file of this patent UNITED STATES PATENTS Re.5,283 Elmer Feb. 23, 1869 25,316 Breisach Sept. 6, 1859 87,156 ElmerFeb. 23, 1869 2,126,150 Stryker Aug. 9, 1938 2,165,820 Smyers July 11,1939 FOREIGN PATENTS 455,567 Great Britain Oct. 23, 1936 OTHERREFERENCES Dolique et al.: Chemical Abstracts (1955), volume 49, No. 21,page 14912f.

1. THE PROCESS OF PREPARING UNSATURATED HYDROCARBONS OF THE GROUPCONSISTING OF ACETYLENE AND ETHYLENE FROM OXYGEN-CONTAINING ORGANICMATERIALS COMPRISING AT LEAST ONE MEMBER OF THE CLASS CONSISTING OF THELIGNINS, THE LIGOCELLULOSES, AND THE CARBOHYDRATES, SAID PROCESSCOMPRISING: REDUCING THE MATERIAL TO A FINELY DIVIDED FORM, RAPIDLYHEATING THE MATERIAL IN A SUBSTANTIALLY INERT GASEOUS ENVIRONMENT TO ASELECTED TEMPERATURE OF AT LEAST 1000* F., MAINTAINING THE MATERIAL ATTHE SELECTED TEMPERATURE FOR A TIME FROM 10**-4 SECONDS TO ABOUT 10SECONDS, THEREBY COVERTING A SUBSTANTIAL PROPORTION OF IT TO A REACTIONPRODUCT INCLUDING A SUBSTANTIAL PROPORTION OF UNSATURATED HYDROCARBON,RAPIDLY COOLING THE REACTION PRODUCT, AND SEPARATING THE UNSATURATEDHYDROCARBON COMPONENT THEREFROM.